The present invention relates to molded articles based on pyrogenically prepared silicon dioxide, process for their production and their use as a catalyst support or catalyst.
Pyrogenically prepared silicon oxides are distinguished by being extremely finely divided and by a correspondingly high specific surface area, very high purity, a spherical particle shape and the lack of pores. Due to these properties, pyrogenically prepared oxides are becoming increasingly important as supports for catalysts; see D. Koth, H.. Ferch, Chem. Ing. Techn. 52, 628 (1980).
Since pyrogenically prepared oxides are particularly finely divided in nature, shaping of such powders to form catalyst supports or catalysts causes some difficulties.
German OLS 31 32 674 discloses a process for the production of molded articles from pyrogenically prepared oxides in which silica sol is uses as binder.
German OLS 34 06 185 discloses a process for the production of molded bodies by using glaze frit powder as a binder and glycerol as a lubricant.
German Patent 21 00 778 discloses employing granules based on pyrogenically prepared silicon dioxides as catalyst support used in processes for the preparation of, for example, vinyl acetate monomer.
These known processes have the disadvantage that the molded bodies so obtained do not have the optimum properties desired, such as, for example, high crushing strength, for certain catalytic reactions, i.g. the preparation of vinyl acetate from ethylene, acetic acid and oxygen or the hydration of ethylene to form ethanol.